Interferon gamma (IFNG) is a cytokine produced by T-lymphocytes and natural killer cells and exists as a homodimer of two noncovalently bound polypeptide subunits. The mature form of each dimer comprises 143 amino acid residues (shown in SEQ ID NO:17), the precursor form thereof includes 166 amino acid residues (shown in SEQ ID NO:18).
Each subunit has two potential N-glycosylation sites (Aggarwal et al., Human Cytokines, Blackwell Scientific Publications, 1992) at positions 25 and 97. Depending on the degree of glycosylation the molecular weight of IFNG in dimer form is 34-50 kDa (Farrar et al., Ann. Rev. Immunol, 1993, 11:571-611).
The primary sequence of wild-type human IFNG (huIFNG) was reported by Gray et al. (Nature 298:859-863, 1982), Taya et al. (EMBO J. 1:953-958, 1982), Devos et al. (Nucleic Acids Res. 10:2487-2501, 1982) and Rinderknecht et al. (J. Biol. Chem. 259:6790-6797, 1984), and in EP 0 077 670, EP 0 089 676 and EP 0 110 044. The 3D structure of huIFNG was reported by Ealick et al. (Science 252:698-702, 1991).
Various naturally-occurring or mutated forms of the IFNG subunit polypeptides have been reported, including one comprising a Cys-Tyr-Cys N-terminal amino acid sequence (positions (−3)-(−1) relative to SEQ ID NO:17), one comprising an N-terminal methionine (position −1 relative to SEQ ID NO:17), and various C-terminally truncated forms comprising 127-134 amino acid residues. It is known that 1-15 amino acid residues may be deleted from the C-terminus without abolishing IFNG activity of the molecule. Furthermore, heterogenecity of the huIFNG C-terminus was described by Pan et al. (Eur. J. Biochem. 166:145-149, 1987).
HuIFNG muteins were reported by Slodowski et al. (Eur. J. Biochem. 202:1133-1140, 1991), Luk et al. (J. Biol. Chem. 265:13314-13319, 1990), Seelig et al., (Biochemistry 27:1981-1987, 1988), Trousdale et al. (Invest. Ophthalmol. Vis. Sci. 26:1244-1251, 1985), and in EP 146354. A natural huIFNG variant was reported by Nishi et al. (J. Biochem. 97:153-159, 1985).
U.S. Pat. No. 6,046,034 discloses thermostable recombinant huIFNG (rhuIFNG) variants having incorporated up to 4 pairs of cysteine residues to enable disulphide bridge formation and thus stabilization of the IFNG variant in homodimer form.
WO 92/08737 discloses IFNG variants comprising an added methionine in the N-terminal end of the full (residues 1-143) or partial (residues 1-132) amino acid sequence of wild-type human IFNG. EP 0 219 781 discloses partial huIFNG sequences comprising amino acid residues 3-124 (of SEQ ID NO:17). U.S. Pat. No. 4,832,959 discloses partial huIFNG sequences comprising residues 1-127, 5-146 and 5-127 of an amino acid sequence that compared to SEQ ID NO:17 has three additional N-terminal amino acid residues (Cys-Tyr-Cys). U.S. Pat. No. 5,004,689 discloses a DNA sequence encoding huIFNG without the 3 N-terminal amino acid residues (Cys-Tyr-Cys) and its expression in E. coli. EP 0 446 582 discloses E. coli produced rhuIFNG free of an N-terminal methionine. U.S. Pat. No. 6,120,762 discloses a peptide fragment of huIFNG comprising residues 95-134 thereof (relative to SEQ ID NO:18).
High level expression of rhuIFNG was reported by Wang et al. (Sci. Sin. B 24:1076-1084, 1994).
Glycosylation variation in rhuIFNG has been reported by Curling et al. (Biochem. J. 272:333-337, 1990) and Hooker et al., (J. of Interferon and Cytokine Research, 1998, 18: 287-295).
Polymer-modification of rhuIFNG was reported by Kita et al. (Drug Des. Deliv. 6:157-167, 1990), and in EP 236987 and U.S. Pat. No. 5,109,120.
WO 92/22310 discloses asialoglycoprotein conjugate derivatives of interferons, inter alia huIFNG.
IFNG fusion proteins have been described. For instance, EP 0 237 019 discloses a single chain polypeptide having region exhibiting interferon β activity and one region exhibiting IFNG activity.
EP 0 158 198 discloses a single chain polypeptide having a region exhibiting IFNG activity and a region exhibiting IL-2 activity. Several references described single chain dimeric IFNG proteins, e.g. Landar et al. (J. Mol. Biol., 2000, 299:169-179).
WO 99/02710 discloses single chain polypeptides, one example among many being IFNG.
WO 99/03887 discloses PEGylated variants of polypeptides belonging to the growth hormone superfamily, wherein a non-essential amino acid residue located in a specified region of the polypeptide has been replaced by a cysteine residue. IFNG is mentioned as one example of a member of the growth hormone super family, but modification thereof is not discussed in any detail.
IFNG has been suggested for treatment of interstitial lung diseases (also known as Interstitial Pulmonary Fibrosis (IPF) (Ziesche et al. (N. Engl. J. Med. 341:1264-1269, 1999 and Chest 110: Suppl: 25S, 1996) and EP 0 795 332) for which purpose IFNG can be used in combination with prednisolone. In addition to IPF, granulomatous diseases (Bolinger et al, Clinical Pharmacy, 1992, 11:834-850), certain mycobacterial infections (N. Engl. J. Med. 330:1348-1355, 1994), kidney cancer (J. Urol. 152:841-845, 1994), osteopetrosis (N. Engl. J. Med. 332:1594-1599, 1995), scleroderma (J. Rheumatol. 23:654-658, 1996), hepatitis B (Hepatogastroenterology 45:2282-2294, 1998), hepatitis C (Int. Hepatol. Communic. 6:264-273, 1997), septic shock (Nature Medicine 3:678-681, 1997), and rheumatoid arthritis may be treated with IFNG.
As a pharmaceutical compound rhuIFNG is used with a certain success, above all, against some viral infections and tumors. rhuIFNG is usually applicable via parenteral, preferably via subcutaneous, injection. Maximum serum concentrations have been found after seven hours. The half-life in plasma is 30 minutes after iv administration. For this reason efficient treatment with rhuIFNG involves frequent injections. The main adverse effects consist of fever, chills, sweating, headache, myalgia and drowsiness. These effects are associated with injecting rhuIFNG and are observed within the first hours after injection. Rare side effects are local pain and erythema, elevation of liver enzymes, reversible granulo- and thrombopenia and cardiotoxicity.
WO 01/36001 discloses novel IFNG conjugates comprising a non-polypeptide moiety attached to an IFNG polypeptide which have been modified by introduction and/or deletion of attachment sites for such non-polypeptide moieties, e.g. PEG and glycosylation sites.
It is well known that when N-glycosylated molecules, such as IFNG, are produced in a glycosylating host not all potential N-glycosylation sites are fully utilized. This means that quite often a mixture of proteins having a varying degree of in vivo N-glycosylation is obtained, which in turn has the consequence that subsequent purification is necessary. Furthermore, it is often time-consuming and cumbersome to separate identical proteins having a varying degree of glycosylation. It has now surprisingly been found that by substitution of one or more amino acid residues located close to an in vivo N-glycosylation site (independently of whether said in vivo N-glycosylation site is naturally occurring in IFNG or whether the in vivo N-glycosylation site has been introduced, such as described in WO 01/36001) it is possible to obtain an increased fraction of fully glycosylated IFNG molecules. In particular, it has been found that changing the naturally occurring N-glycosylation site N-Y-S at positions 97, 98 and 99 of hIFNG to N-Y-T gives rise to a dramatically increased fraction of fully glycosylated IFNG molecules.
Furthermore, it is known that when IFNG is produced in mammalian cell lines a heterogenous population of IFNG polypeptides is obtained due to C-terminal truncation of the IFNG polypeptide (reviewed in Lundell et al. Pharmac. Ther. 64, 1-21, 1994). Clearly, this constitutes a severe problem in that valuable polypeptide material is lost and, further, it is necessary to carry out time-consuming and cumbersome purification in order to obtain a homogenous population of active IFNG polypeptides having the desired length. Most likely, this truncation is effected by endo- and/or exoprotease activity produced by the host cell.
Thus, it is also an object of the present invention to provide IFNG fragments and variants thereof, which are not prone to C-terminal truncation during production, purification or storage.